From: Milton Aupperle <milton@outcastsoft.com>

Date: July 7, 2007 4:14:51 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] guiding with Astro IIDC


Phil.


On 7-Jul-07, at 2:58 PM, Phil Houston wrote:

Milton,


The discussion about auto-guiding has raised a question about using Astro IIDC for guiding my scope.  I use a small 90 mm scope and a  210 mm f/5.6 zoom camera lens attached to a DMK camera for auto-guiding through a GPUSB to an ST-4 compatible connection.  Past attempts to use Astro IIDC resulted in a failure to calibrate possibly because of the short focal length of the guide scope and slow speed of the telescope drive.


1) Which Version of Astro IIDC is this with 3.x.x? The new GPUSB units broke compatibility with previous versions of Astro IIDC, but the current version of 3.02.01 works fine with them.


2) What mount are you using (CG5, HEQ6, Meade LX200 etc etc.)?


3) What Guide Rate did you set in the hand controller for the mount? All the mounts that I have seen allow you to specify what guide rate they use, which usually 0.25 to 2x rates in the hand controller. The GPUSB is just an electronic switch which turns the motors on or off. It does not control the rate that the motors turn at, which is why you need to set this with the hand controller. For short focal lengths like 210 mm, you should be using at least 1x. For the 400 lens mm, I use 1x and start off at 10 seconds for calibration.


The reason why you need to match the guide rate and the guide focal length  is simply because you want  Astro IIDC to quickly correct deviations. If it takes 30 seconds to correct from some deviation, then it's basically useless because it may be under or over correct the next time it needs to move. You want the corrections to be as fast as possible before it gets out of hand.


With a 210 mm lens on a DMK camera each pixel represents 5.3 arc seconds. At 1x guide rate, the motors move the scope 15 arc seconds in RA and at 0.1x guide rate, it moves 1.5 arc seconds.


So if your using a 0.1x guide rate, it will take the motor 3.53 seconds of time to make a star (Declination 0 degrees) move 1 pixel on the guide scope camera. To make it move the required 50 pixels for Calibration at that rate will take 176.65 seconds and that will never work. So you need to increase the guide rate to compensate for this and 1x will work great with a GPUSB.


This may have caused the program to either time out or think the drive was not functioning, I don't know.  It is possible to move the scope using the manual controls in Astro IIDC.  I tried using PHD for guiding and initially had the same results (calibration failed) until I found a setting to increase the length of time the drive signal was sent to the scope.  Calibration was then successful  and I can finally auto-guide using my Mac.


Astro IIDC 3 has this too, see page 16 and 17 of the embedded Astro IIDC Help pdf.


My question is,  does Astro IIDC have a way to increase the length of time the drive signal is sent to the scope? 


Yes. It's right in the control window in the pop up menu entitled ""Start Time:"" You can set it to it up to 30 seconds initially and it will adjust this value until it runs up to 60 seconds. If Astro IIDC can't get any movement after moving for up to 60 seconds, it gives up. It does print out information on this in the Console.log window and warns you that this has happened.


I do enjoy the capabilities and ease of use of your program and hope I can use it for imaging DSO's as well as the Moon and planets.  My apologies in advance if I have missed a reference to this in the manual.


The manual is re-written for any new feature in a 0.x.00 release too - so you people really shoudl rad through it.


Last month I tested the auto-guiding capabilities of the system and produced the images linked below.  For imaging DSO's I used a first generation  MacBook and Parallels to run AstroArt 2.0 in order to capture images with an old StarlightXpress MX916 camera (Nebulosity doesn't work with the oldies).  No filters were used for the luminance and I kinda skimped on the color.  Guiding is done on the Mac side with PHD right now and hopefully with Astro IIDC someday.  I used to image with a  500 MHz G3 iBook using Virtual PC for the PC stuff but did not have a Mac program to guide with back then so I don't know if the G3 could handle it all.


A 500 mhz G3 may be too slow, unless you cut it back to around 7.5 fps frame rates for guiding. A 500 mhz G4 would be fast enough because of the Altivec processor.


I noticed that even with my small guide scope, there was a slow misaligning taking place during the exposures evident by the shifting frames when stacked.  I can't believe tube flexure is the cause.  More likely loose components in the the cheap camera lens or the single 1/4 20 mounting screw slipping.  The effect has been cropped out in the images below but the stars show the slight drift.


Don't forget about Mirror Flop on the primary too, especially 10 inch or larger CAD without good mirror locks. My MAK127 mm scope had that really bad. That's one of the reasons using small MAK / CAD scopes for guiding is not usually working great either, because you now have two flops. Refractors are usually better as guiders.


Milton J. Aupperle

President

ASC - Aupperle Services and Contracting

Mac Software (Drivers, Components and Application) Specialist

#1005 - 815 14th Avenue. S.W.

Calgary Alberta T2R0N5

1-(403)-229-9456

milton@outcastsoft.com

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